Standard ball pens are constructed with tubular ink reservoirs that have typical inside diameters of 0.080 inch to 0.085 inch. The physical properties of the ink coupled with the small tubing diameter prevent the ink from running out of the tube when the pen is disposed in an attitude with the pen tip above the open end of the tube.
One common problem of such pens is that they do not write on vertical surfaces or with the tip up, since the ink does not retain suitable contact with the writing tip. Many attempts have been made to provide a pen that will write on vertical surfaces or on a surface when the pen tip is above the open end of the pen. Two such developments provide a ball point pen with an internal gaseous charge that urges the ink against the ball. See U.S. Pat. No. 2,500,998 (Morris) and U.S. Pat. No. 2,560,811 (Morris). However, such pressurized pens often require special ink to prevent leakage around the ball.
U.S. Pat. No. 2,444,004 (Chesler) discloses a writing instrument wherein a mechanical pressure device exerts a constant pressure against a lengthwise portion of a flexible ink reservoir sac. The pressure device, however, does not exert a pressure on the entire cross sectional area of the reservoir sac, nor does it exert its pressure in the direction of the writing tip itself. Thus, a substantial quantity of ink, trapped in the reservoir sac above the pressure means may never flow into the writing tip assembly.
Today, many commercial recorder instruments require the utilization of a short axial length ball point pen attached to a recorder pen arm. To be commercially valuable, such pens must contain a large volume ink supply, or else the frequent refilling of the ink supply will cause both delay and interruption of instrument operation.
Further, such a short axial length ball point pen must be leak-proof both at the writing tip and at the opposite end thereof so that it may be shipped and utilized without fear of damage due to such leakage. Moreover, a short axial length ball point pen capable of writing on any surface regardless of the manner in which the pen body is disposed is of even greater commercial value. Such a pen is made even more competitive if it does not require the utilization of special ink to prevent leakage around the ball.
Thus, it is an object of this invention to provide an inexpensive, short axial length, wide diameter ball point pen, containing a large volume of conventional ink, that will be of great commercial use in the recorder instrument field.
Another object is to provide a short axial length ball point pen that is substantially leak-proof at both ends thereof.
A more specific object of the present invention is to provide a short axial length ball point pen that exhibits the characteristic of being able to write on any surface regardless of the positioning of the writing end and opposite pen end.